The annual blood harvest of the horseshoe crab

Every year, horseshoe crabs are gathered up and transported to a
laboratory where up to 30 percent of their blood is removed while
they are still alive. Once the blood has been collected, the crabs
are taken back to the water and released. Why? Because horseshoe
crab blood has a nifty ability to detect contamination in
pharmaceutical products.

Pharmaceutical companies takes great care to produce drugs,
vaccines and medical devices that are sterile. There is a
particular type of bacteria -- gram-negative bacteria -- that can
be harder to detect and resistant to drugs. Gram-negative bacteria
-- so called because they do not turn purple in the Gram staining
bacteria identification process -- cause diseases such as spinal
meningitis, typhoid, and toxic-shock syndrome. On the cell walls of
gram-negative bacteria are found endotoxins. Even after substances
are sterilised, they can still contain some bacterial components
such as endotoxins. However, the horseshoe crab's blood is adept at
detecting these.

Although horseshoe crabs resemble crustaceans, they actually belong to a subphylum
Chelicerata, meaning they are more closely related to spiders and
scorpions. Fossils show that the horseshoe crab dates back to
around 450 million years ago and has changed very little over the
last 250 million years.

This isn't the only remarkable thing about the horseshoe crab.
Its blood is a distinctive blue colour thanks to the fact that it
contains copper-rich haemocyanin as opposed to iron-rich
haemoglobin. The blood also contains amoebocytes, which play a similar role to
white blood cells. When a crab is wounded, the amoebocytes swam to
the area and coagulate to form a viscous gel surrounding the
invading bacteria. This blood-clotting mechanism ensures the crab
doesn't develop an infection.

The effect was initially reported in 1956, when Fred Bang noted that even if the gram-negative bacteria
were dead, the crabs' blood would still coagulate. This is because
they were detecting the residual endotoxins.

In order to turn crab's blood into a commercial impurity
detector, it is first of all centrifuged to separate the
amoebocytes from the liquid plasma. These are then freeze-dried and
processed by pharmaceutical companies to create limulus amebocyte
lysate (LAL). A litre of LAL costs around $15,000.

A lab wanting to test a substance needs to reconstitute a vial
of the freeze-dried LAL with endotoxin-free water and add it to a
sample solution in a clean test tube. The mixture is then incubated
for an hour at 37 degrees centigrade. The mixture is then examined
for gel formation. If sufficient endotoxins are present, a firm gel
will be formed that will remain in place when the test-tube is
turned upside down.

Comments

This is a terrbile process. The liquid crystal is much cheaper and less drastic on the crab population. The crabs may survive the process, but how will a crab with 30% or more of their blood taken forcibly, put into an environment that will shock the delicate internal balance of their biology, survive in the wild? This is a terrible, inhumane crime against nature and must stop.

Sarah

Jan 18th 2012

In reply to Sarah

i couldn't agree more.

alfred threfall

Aug 10th 2012

horseshoe crab

sandy

May 5th 2012

It's awesome! It can kill bacteria and helps human beings. Who says it is a crime?

Michelle

Sep 30th 2012

It's awesome! It can kill bacteria and helps human beings. Who says it is a crime?

Michelle

Sep 30th 2012

In reply to Michelle

Michelle, you should read more carefully. It doesn't kill the bacteria, it simply detects them. Why would you choose a cruel process over one that doesn't harm living creatures?

Zelda

Mar 11th 2013

"it helps human beings" <--- I don't think a species with a population over 7 billion need quite as much help as those being strapped in and bled nearly (and sometimes completely) to death, and who nearly got their species wiped out in the first place.